Method for double wire sternotomy suture

ABSTRACT

A sternotomy suture comprises a loop which passes around a split sternum and is twisted until double cabling begins at which point the suture is fastened to itself. The loop preferably comprises a single strand of wire with one end welded to an intermediate point of said strand leaving a portion available for connection to the needle. A curved needle having a cutting tapered point is swaged to the free end of the single strand. Initially the wire is passed around the split sternum and the needle then removed with a pair of diagonal cutting pliers. A twisting tool, having a handle and a hooked portion, passes through the two free loops on opposite sides of the sternum. Twisting force is applied to the tool and transmitted through the hook to the suture causing it to twist and cable. The suture reaches its critical length L crit  when the loop is fully cabled but before double cabling begins. At the onset of double cabling the loop reaches its maximum tension T crit . This is the signal to the surgeon to stop turning and to fasten the loop to itself. As a consequence, the resulting sternotomy suture is applied with optimal force. The loop is not too tight to cause discomfort and possible complications; nor is the loop too loose thereby creating an inferior bond.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims the priority of, ourprovisional patent application entitled DOUBLE WIRE STERNOTOMY SUTUREfiled on Apr. 4, 1997 and issued Provisional patent application Ser. No.60/042,650, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a double wire sternotomy suture apparatus andmethod for closing a split sternum employing optimal force in theprocess.

2. Description of Related Art

Sternotomy sutures are stainless steel sutures used to lace up thesternum after a surgery that requires cutting the length of the sternumto gain access to the chest cavity. A sternotomy is routinely performedwhen heart surgery is required. Sternotomy sutures are available from anumber of companies such as the MYO/WIRE® suture available from A & EMedical Corporation, 5206 Asbury Road, Farmingdale, N.J. 07727.

In general, history has shown that sternotomy wires are the most safeand effective method for closing the sternum during the period of timenecessary for the sternum halves to heal together. The wires are usuallyleft implanted for life because they are atraumatic and removal couldcause difficulties especially if bone has grown around the wire.Surgeons prefer the use of wires because they are simple to apply,produce the least post surgical complications, and are relativelyinexpensive. The prior art methods, however, have presented someinstallation and post operative problems described below.

The first major problem is that band tightening by twisting wirestogether with a pair of pliers is an inexact method. The surgeon has todevelop a very sensitive "feel" for how much torque he or she can applyto properly tighten the band without breaking the wire. Consequently, itis common for a great number of suture wires to break duringinstallation. As a counter to this, new wires have been developed whichare more resistant to breaking during band tightening. A wire break,however, generally requires the surgeon to undo all finished sutures andstart the process all over again. For fear of breaking a wire, a surgeonwill tend to under torque the suture resulting in less than optimalclosure pressure on the sternal knit line. This can lead to dehiscenceproblems.

A second major prior art problem relates to the consequence of movementalong the sternum knit line. For a number of reasons, many patientsdevelop a chronic cough after surgery that places a heavy stress on thesuture wire bands. Stress is even greater for heavy, large chestedpersons. This can cause the bands to loosen or break. The resultingdehiscence (movement along the sternum knit line) is very bad especiallyif infection sets in. This condition usually requires a completely newoperation to replace and tighten new sternal suture wires along withaggressive antibody treatment for the resulting infection. A reasonableestimate is that dehiscence and/or sternal infection complications incurin 1.5 to 2.0% of all heart surgery patients. Hospitals estimate thatthe additional cost to treat each of these patients averages $20,000 perpatient or $300,000 minimum cumulative cost to a hospital performing1,000 heart operations a year. Hence, an improvement in sternal closurethat reduces dehiscence could be very cost effective and desirable.

The prior art patent literature discloses a handful of loop typesurgical devices for other purposes. Note, for example, U.S. Pat. No.5,259,846 entitled LOOP THREADED COMBINED SURGICAL NEEDLE-SUTURE DEVICE.That disclosure describes incorporating two ends of a looped suture intoa surgical needle to facilitate quick knotting and tying as may beneeded during critical surgical procedures.

U.S. Pat. No. 3,762,418 entitled SURGICAL SUTURE discloses a doublestrand, but not looped, suture preferably having needles at both ends.This enables double suturing simultaneously in a single procedure.

U.S. Pat. No. 5,089,012 entitled SURGICAL SUTURE, IN PARTICULAR FORSTERNOTOMY CLOSURE, discloses a typical prior art single needle surgicalsuture incorporating a single monofilament portion.

U.S. Pat. No. 4,602,636 entitled SUTURE WIRE WITH INTEGRAL NEEDLE-LIKETIP is of possible relevance for its teaching of a suture having anintegrated needle tip therein attached to a single homogenous piece ofwire.

U.S. Pat. No. 5,092,868 entitled APPARATUS FOR USE IN THE TREATMENT OFSPINAL DISORDERS teaches an endless loop of wire flattened to form twostrands which are employed along with a T-shaped handle to attach abracket to the spinal cord. It is noted, with interest, however, thatthe two portions of the strands are mechanically held next to each otherand can be manipulated as a unit to guide it through a spinal opening.

U.S. Pat. No. 5,501,688 entitled SURGICAL DEVICE FOR MANIPULATING WIREdiscloses a tool and method for tightening a single strand suture havingloops at both ends.

Lastly, the following patents are all cited as describing the generalstate of the art and appear to be of lesser relevance to the disclosedinvention: U.S. Pat. Nos. 4,201,215; 4,512,346; 4,535,764; 4,813,416;and, 4,901,721.

Insofar as understood, none of the disclosed prior art appears to teach,hint or suggest a loop suture suitable for enclosing a split sternumsuch that optimal force is applied. Moreover, none of the prior artappears to disclose a method and procedure for fastening a suture toitself at the optimal tension T_(crit) when double cabling begins.

It was in the context of the foregoing that the present invention arose.

SUMMARY OF THE INVENTION

Briefly described, the invention comprises a sternotomy suture in theform of a loop which can be employed to close a split sternum withoptimal retaining force. The loop is preferably formed from a singlestrand of wire in which one free end is welded an inch or two below theother free end to form a loop. A standard sternotomy needle having acurved, tapered end is swaged to the remaining free end of the strand.

The procedure comprises the following steps. First, the needle is passedaround the split sternum so that a portion of the loop appears on bothsides. Second, the free end of the needle is snipped off between theweld and the needle leaving only the loop intact. Third, a twisting toolhaving a handle and a hooked portion passes through the two openportions of the loop on opposite sides of the sternum. Fourth, the toolis rotated until the loop has been fully absorbed in a single cable atL_(crit). Fifth, continued twisting of the tool causes the suture tobegin double cabling. This occurs at the optimal tension T_(crit). Atthis point the surgeon fastens the loop to itself and snips off theremaining portions. The force applied to the split sternum is optimaland sufficient to close the gap, yet not too tight to cause problems.

These and other features of the apparatus and procedural method may bemore fully understood by reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the preferred embodiment of the double wiresternotomy suture showing the needle attached to the loop portion of thesuture.

FIG. 2 illustrates just the loop portion, formed from a single piece ofwire, welded to itself prior to attachment of the needle section.

FIG. 3 is a detailed view of the welded portion of the loop sutureillustrated in FIG. 2.

FIG. 4 illustrates the first two steps of the method according to thepreferred embodiment of the invention in which the surgical needle hasbeen passed around the split sternum and is subsequently cut off by apair of diagonal pliers.

FIG. 5 illustrates the next step of the procedural method in which thehook portion of a twisting tool is passed through the two open portionsof the suture loop.

FIG. 6 illustrates the next step of the procedural method in which thetwisting tool is turned to cause the surgical loop to begin cabling.

FIG. 7 illustrates the next step of the procedural method in which theloop suture is fully cabled at L_(crit).

FIG. 8 illustrates the next step of the procedural method in which theloop suture begins to double cable at which point it is cut and fastenedat the optimal tension T_(crit).

FIG. 9 illustrates the last step of the procedure with the surplus wirecut off.

FIG. 10 illustrates an alternative embodiment of the invention in whichthe double suture is a continuous loop which is connected to a separateleader portion having a different diameter.

FIG. 11 illustrates another alternative embodiment of the invention inwhich the double suture is in the form of a loop in which the two freeends of a single continuous piece of suture wire overlap and abut with aseparate leader portion having a different, larger diameter and wherethe three segments are welded to each other in that relationship.

DETAILED DESCRIPTION OF THE INVENTION

During the course of this description like numbers will be used toidentify like elements according to the different figures whichillustrate the invention.

The preferred embodiment 10 of the invention is illustrated in FIG. 1.The basic elements of the invention 10 are a loop section 12 and aneedle section 14.

The needle section 14 preferably comprises a channel needle having a tip16, a curved midportion 20, and a base 18 that is swaged to the free endof the strand 28 as illustrated in FIGS. 2 and 3.

The loop portion 12, illustrated in FIGS. 2 and 3, is preferably formedfrom a single strand of stainless steel suture wire USP#6 or #8 asrequired. The single strand is doubled back onto itself such that onefree end is welded to an intermediate portion of the strand at weldlocation 26. This results in a loop suture having a first leg 22a, arounded end section 24, having a radius R_(l) and a second return leg22b. The length of the loop portion L_(l) from the weld section 26 tothe curved end 24 is preferably about 11.86 inches. The remaining strand28 has a length of L_(ss) of roughly 2.00 inches. The strand ofstainless suture wire prior to its forming as shown in FIG. 2 isapproximately 22 inches in length. The radius R_(l) of the curved end 24is preferably about 0.25 inches. The space between legs 22a and 22b forman opening 46.

The weld section 26 of the loop 12 is shown in detail in FIG. 3. Theweld 26 is preferably formed of stainless steel welding material andswaged to a tapered shape as shown in order for a smooth transition fromthe needle section 12 to the loop section.

The preferred procedural method steps of the invention 10 areillustrated sequentially in FIGS. 4-9. As shown in FIG. 4, the firststep 30 of the procedure is to pass the needle 14, in a conventionalmanner, around the sternum 32 between the intercoastal spaces. Thesternum 32 is shown having a split or gap 34 therein which needs to beclosed in a safe manner.

The second step of the procedure, also shown in FIG. 4, and identifiedas element 30, is to cut the needle strand 28 between the weldment 26and the needle 14 so as to separate the needle 14 from the rest of theloop 12. A pair of diagonal cutting pliers 36, or similar tool, are usedto snip the needle 14 from strand 28.

In a third step 38, illustrated in FIG. 5, a twisting tool 40 isemployed to twist the two free loop ends 62, 64 together. After theneedle 12 has been removed, as illustrated in the first and second step30 of FIG. 4, the two wires 22a and 22b at the weldment 26 are spreadapart to form a first loop section 62 with a gap therein 46. A secondloop section 64 is formed naturally on the opposite side from thecurved, rounded end 24 and also includes a gap 46 therein. Twisting tool40 includes a handle section 42 and a hook section 44. The hook section44 is passed through the gap 46 in the first loop 62 and then throughthe other gap 46 in the second loop 64 so that both loops 62 and 64 areengaged as shown in FIG. 5.

The next, or fourth, step 48 in the procedural method, is illustrated inFIG. 6. The tool 40 is rotated in the direction of arrow 50 causing theloop section 12 to twist or cable in area 52 and exert upward anddownward forces as illustrated by arrows 54. Twisting tool 40 continuesto rotate in the direction of arrow 50 to twist all four wires (22a,22b) until the band 12 around the sternum 32 becomes tight and the gap34 disappears.

The next, or fifth, step 56 in the preferred procedural method isillustrated in FIG. 7. The cabling 52 continues until the loop 12 isfully cabled at a certain critical length referred to as L_(crit). Aninteresting phenomenon has been observed at this point. It has beennoted, for both single and double suture wires, that as the wires aretwisted, cabling 52 of the wires starts at a random location, thensimultaneously progresses towards the twisting tool 40 at one end anddown towards the sternum 32 at the other in the direction of doublearrow 54. During this process nearly all of the twisting torque T goesinto the cabling effect 52 and not into the tightening of the band 12around the sternum 32. As the cabling 52, however, fills the spacebetween the twisting tool 40 and the sternum 32, the band loop 12 closesand then begins to tighten when the cabling 52 comes into contact withthe sternum 32. It is the rotation of the cable bundle 52 adjacent tothe sternum 32 that tightens the band. The forces within the cablebundle 52 are somewhat complex due to the cable construction. In generalterms, however, it is the maximum shearing stress within this last cablebundle 52, closest to the sternum 32, that dictates how much the bandcan tighten before the wire in the loop 12 breaks at the cable knot 52.Elastic theory suggests that the maximum shear stress is proportional tothe inverse of the cable diameter cubed. Hence, for a given torque T themaximum shear stress reduces dramatically as the diameter of the cabling52 increases. The cable diameter of a double wire twist is about twicethat for a single wire twist. Accordingly, for a given torque the shearstresses for a double wire are (1/2)³ or 1/8^(th) of those for a singlewire. What this implies for a surgeon is that a double wire can betorqued to a band loading much more than double that of a single wire,perhaps as much as 8 times higher.

Accordingly, what is desired is a form of torque limiting to preventinjury to the sternum 32. In particular, it would be desirable to allowa surgeon to install a double wire, such as loop 12, without fear ofbreaking the wire or causing injury to the patient. One approach mightbe, for example, to build in some form of weakness into the suture thatwould cause the cabling to break at a predetermined location and torquevalue. During experimentation, however, it was observed that once thelength of the cable between the twisting tool 40 and the sternum 32exceeded a certain critical length L_(crit), the cable 12 could only betwisted by a limited amount of torque T_(crit) before the cable 12starts to twist around itself and form a double cable 60. This comprisesthe sixth step 58 in the process as illustrated in FIG. 8. It has beenfurther determined that the size of wires most advantageous forsternotomy sutures are USP#5 through USP#8. This T_(crit) producesadequate band tension without fear of breaking the wires 22a, 22b orinjuring the patient. It has been found that the optimal wire lengthrequired to guarantee a cable length greater than L_(crit) is one thatgives a cable length greater than 2 inches for the largest patient.Therefore, employing the preferred procedural method of the presentinvention, all the surgeon has to do is twist the double suture 12 untilit starts to produce double cabling 60 as shown in FIG. 8.

The cable is then trimmed to a short length as per standard surgicaltechniques as shown in the last step 66 in FIG. 9.

It is also been determined that the double cabling effect will alsooccur with single wires. In such a case, the surgeon twists the wireuntil it starts to double cable. However, because of the lack oftorsional rigidity, the band tension is inadequate at that point.Accordingly, the surgeon has to cut the cable short and then applyadditional torque T to tighten the band. Therefore, at that time, thesurgeon has to use critical judgment to determine when the band is tightenough without breaking the band. It has, therefore, been determined,that double wires, such as loop 12 avoids this additional step and ismuch more reliable.

The alternative embodiment 100 of the invention is illustrated in FIG.10. The invention, according to alternative embodiment 100 comprises acontinuous loop 102, a separate leader section 112 and a curved needle104. Curved needle 104 includes a tip 106, a midsection 110 and a buttsection 108. The butt section 108 of needle 104 is swaged to the leadersection 112 in the same manner that needle 14 is attached to section 28of the preferred embodiment 10. The leader section 112 of alternativeembodiment 100 is welded to continuous loop section 102. The advantagesof alternative embodiment 100 is that the diameter of the wire in thecontinuous loop section 102 can be different from the diameter of thewire in the leader section 112 so that the diameter of the leadersection 112 better matches the diameter of the butt section 108 ofneedle 104. This permits the leader section 112 to be stronger than thewire in the loop section 102. When leader section 112 is welded to loopsection 102 the attachment point is taped down so that the transition isrelatively smooth and friction free during use.

In a second, alternative embodiment 200 illustrated in FIG. 11, thecontinuous loop 202 is formed from a single strand of suture wire,preferably about 24 inches long, in which the two free ends 204a and204b are parallel to and abut each other. The separate leader strand 112also overlaps and abuts with ends 204a and 204b. The three wires 112,204a and 204b are welded together in an overlapping fashion. Thisarrangement permits a somewhat larger leader wire 112 to be welded to asomewhat smaller diameter wire 202. Therefore, it is possible to producea double wire suture 200 having a needle 104 and a leader 112 that arelarger in diameter and, therefore, stronger than the double sutureportion 202. Accordingly, different size needles 104 can be attached tosutures 202 having different diameter sizes.

In summary, the foregoing double wire sternotomy suture apparatus andprocedural method have several advantages over the prior art. First, themethod is relatively simple and reliable. As a result, the surgeon doesnot have to repeat the procedure as often as was required in the priorart due to wire breakage. Second, the pressure applied to the sternum isoptimal and predictable. The pressure placed on the sternum issufficient to close the gap without crushing the intersection. Third,dehiscence, i.e., movement along the sternum knit line, is minimized. Asa result, it is estimated that the incidence of dehiscence and/orsternal infection should drop substantially thereby reducing patientmorbidity and hospital costs.

While the invention has been described with reference to the preferredembodiment of the sternotomy suture apparatus and its related preferredmethod of implementation, it will be appreciate by those of ordinaryskill in the art that modifications can be made to the structure andsteps of the invention without departing from the spirit and scopethereof.

we claim:
 1. A method of suturing a split sternum having a gap thereinemploying a suture in a form of a loop and a needle attached to saidsuture, said method comprising steps of:a. passing said needle and atleast a portion of said loop around said sternum; b. cutting off saidneedle; c. attaching a tool through said loop, wherein said tool passesthrough at least two loop portions of said loop; d. twisting said tooland said loop portions until double cabling begins which corresponds toa constant force applied to said sternum; e. fastening said loop,whereinsaid loop tightly closes said gap in said sternum.